1. Field of the Invention
The present invention relates to a polishing method and a polishing apparatus for polishing and flattening a surface (surface to be polished) of a substrate, such as a semiconductor wafer.
2. Description of the Related Art
A multi-step chemical mechanical polishing (CMP) process is known in which a surface (surface to be polished) of a substrate, such as a semiconductor wafer, is polished in a plurality of polishing steps. For example, in the case of polishing a surface of a substrate by a two-step polishing process, the first-step polishing may be carried out by using a polishing liquid (slurry) having a high polishing rate, though having a low irregularities eliminating property, and carrying out the second-step polishing by using a polishing liquid having a low polishing rate, but having a high irregularities eliminating property. By earning a polishing amount by the first-step polishing, the total polishing time can be shortened.
In carrying out a multi-step polishing process for a plurality of substrates, such as semiconductor wafers, in a successive manner, it is a conventional practice to measure surface conditions, such as a thickness of a film, of each substrate before polishing, between polishing steps and after polishing, and feed back a measured value to optimally modify (renew) polishing conditions, i.e., polishing recipe (prescription of pressure distribution, polishing time, etc), for the next substrate or a later Nth substrate.
Measurement of the surface conditions of a substrate, such as a semiconductor wafer, is commonly carried out with a measurement section called ITM (in-line thickness monitor). An ITM is generally disposed outside a polishing section which carries out polishing; and in order to measure the surface conditions of a substrate with the ITM, it is necessary to take the substrate out of the polishing section, and clean and dry the substrate. Thus, in carrying out a multi-step polishing process successively for a plurality of substrates, it is common practice to take a substrate out of a polishing section between polishing steps or after polishing, and clean and dry the substrate to measure the surface conditions of the substrate with an ITM.
The operations of taking a substrate out of a polishing section, and cleaning and drying the substrate, if carried out for every measurement of the surface conditions of a substrate such as a semiconductor wafer, take a great deal of time. Especially in the case of carrying out a multi-step polishing process successively for a plurality of substrates, it is a conventional practice to measure the surface conditions of each substrate with an ITM even between the respective polishing steps and feed back the measurement results to optimally modify (renew) the polishing recipe. Thus, the time taken for measuring the surface conditions of a substrate increases the total polishing time, causing lowering of the throughput.